1. Technical Field
The present invention relates to an optical system for a camera, and more particularly, to an optical system for a camera capable of being manufactured in a small size in order to be mounted in a mobile device and implementing a high resolution.
2. Description of the Related Art
Recently, as the use of a mobile communication unit such as a mobile communication terminal, a personal digital assistant (PDA), and a smart phone increases and a service provided through a communication technology is verified, in addition to a basic communication function, various types of additional functions have been mounted. Among them, the mounting of a camera for simple photographing has been generalized.
Further, recently, in an optical system of a camera used in a mobile device such as a cellular phone, the number of pixels has increased to eight million pixels or more in excess of five million pixels. In addition, a view angle of 70 degrees or more wider than a general view angle of about 60 degrees has been demanded.
However, when a view angle of a lens is increased, an incident angle of a light ray incident to a lens surface cannot but be increased, such that performance deterioration may be intensified even in the same manufacturing tolerance. In addition, as a pixel size of a sensor is decreased, a required spatial frequency is increased, such that an optical system having a high resolution is required.
When the spatial frequency is increased and the resolution is increased, sensitivity to the manufacturing tolerance of the optical system cannot but be increased. Therefore, the development of the optical system having a high resolution and capable of decreasing the sensitivity has been required.
Meanwhile, a high-pixel optical system supporting eight million pixels, which is an optical system for a camera according to the related art, is mainly configured of four sheets of lenses (having a pixel size of 1.4 μm or more), wherein first and second lens of the four sheets of lenses are in charge of the entire refractive power of the optical system, and third and fourth lenses thereof are in charge of image surface field curvature and distortion to correct aberration that is not corrected by the first and second lenses.
In addition, as the first and second lenses, a crown or flint based glass lens is used. Particularly, the second lens has negative refractive power and is made of the flint based glass material to compensate for longitudinal chromatic aberration. However, it is difficult to satisfy conditions such as miniaturization and cost reduction with an optical system design considering a manufacturing cost of an optical system for a mobile camera.
Particularly, due to characteristics of the optical system for a camera applied to the mobile device, a plastic lens is mainly used in consideration of mass production, size, weight, and cost. Therefore, it is difficult to satisfy optical performance and compensate for chromatic aberration with a general optical system design.